Variable valve timing apparatus

ABSTRACT

An intake VVT mechanism includes: link mechanisms and connected to an intake camshaft and operated to change a phase of an intake valve; and a control pin sliding on a guide plate along a guide groove to allow the link mechanism to operate; a control pin sliding on the guide plate along a guide groove to allow the link mechanism to operate. The control pin is detached from an end of the guide groove when the control pins and are moved in a direction allowing the phase to be retarded until the control pin abuts against an end of the guide groove.

TECHNICAL FIELD

The present invention relates to a variable valve timing apparatus. In particular, the invention relates to a variable valve timing apparatus that changes when a valve is should be opened/closed by an amount of variation according to an amount of operation of an operation unit (a link mechanism).

BACKGROUND ART

VVT (Variable Valve Timing) has conventionally been known that changes the phase (crank angle) in (at) which an intake valve or an exhaust valve is opened/closed, according to an operating condition. Generally, the VVT changes the phase by rotating, relative to a sprocket or the like, a camshaft that causes the intake valve or exhaust valve to open/close. The camshaft is rotated hydraulically or by an electric motor or the like. In the case where the electric motor is used to rotate the camshaft, the torque for rotating the camshaft is difficult to obtain, as compared with the case where the camshaft is hydraulically rotated. Therefore, in the case where the electric motor is used to rotate the camshaft, the torque of the electric motor is transmitted via a link mechanism or the like to the camshaft, thereby rotating the camshaft.

Japanese Patent Laying-Open No. 2005-048706 discloses a valve timing adjustment device employing a link (a link mechanism) to transmit a torque to a driven shaft (a cam shaft) to adjust when a valve should be opened/closed. The publication describes that the valve timing adjustment device is provided in a transmission system transmitting a driving torque of a driving shaft to a driven shaft driving and thus opening and closing at least one of intake and exhaust valves in an internal combustion engine to adjust when at least one of the valves should be opened/closed. The valve timing adjustment device includes a guide member forming a guide passage of a generally constant width, a movable body with which the guide member is engaged on both sides in the width direction of the guide passage to be capable of relatively sliding to the guide member in the direction in which the guide passage extends, a phase changing mechanism formed of a plurality of links and composing a limiting link with the guide member and such movable bodies as the movable bodies are each engaged with an associated link to change the rotation phase of the driven shaft to the drive shaft in accordance with relative sliding of the movable bodies to the guide member, and a torque transmission unit transmitting a control torque to the guide member. The guide member forms the guide passage, which extends with an inclination relative to a radial axis and has a variable distance to a centerline of rotation, as seen in the radial direction, and the guide member rotates relative to an associated link as the control torque is transmitted.

As described in the publication, the valve timing adjustment device includes a guide member that forms a guide passage extending with an inclination relative to a radial axis and having a variable distance to a centerline of rotation, as seen in the radial direction and engages with a movable body on both sides in the width direction of the guide passage. Thus from the torque transmission unit to the guide member the control torque can be transmitted to rotate the guide member relative to an associated link. This can help to slide the movable body relative to the guide member to change the phase of the rotation of the driven shaft and as a result adjust when at least one of the intake and exhaust valves should be opened/closed.

However, if, a valve timing adjustment device employs a plurality of link mechanisms as described in the publication to change when a valve should be opened/closed, however, it is difficult to detect whether the link mechanisms have failure; if one of the plurality of link mechanisms is damaged, the other link mechanisms can change when the valve(s) should be opened/closed, and the valve(s) can be opened/closed as controlled.

DISCLOSURE OF THE INVENTION

The present invention contemplates a variable valve timing apparatus capable of detecting failure.

The present invention in an aspect provides a variable valve timing apparatus changing when at least one of an intake valve and an exhaust valve should be opened/closed. The variable valve timing apparatus includes: a first operation unit provided to change when at least one of the intake and exhaust valves should be opened/closed by an amount of variation depending on an amount of operation thereof; a second operation unit provided to change when a valve identical to at least one of the intake and exhaust valves controlled by the first mechanism should be opened/closed by an amount of variation depending on an amount of operation thereof; and a limiter unit limiting the first operation unit in operation such that the first operation unit is operable only within a range smaller than the second operation unit is operable.

In accordance with the present invention when at least one of intake and exhaust valves should be opened/closed is changed by an amount of variation depending on an amount of operation of a first operation unit (e.g., a first link mechanism) and a second operation unit (e.g., a second link mechanism). If one of the operation units is damaged and cannot operate normally, the other operation unit can change when at least one of the intake and exhaust valves should be opened/closed. The first operation unit can operate within a range limited by a limiter unit to be smaller than the second operation unit can. If the first operation unit is not damaged or the like and normally operates, when at least one of the intake and exhaust valves should be opened/closed can be changed until the first operation unit is limited in operation by the limiter unit. In contrast, if the first operation unit is damaged and cannot operate normally, the first operation unit is not limited in operation by the limiter unit and when at least one of the intake and exhaust valves should be opened/closed can further be changed beyond the first operation unit's operable range. As such, whether the first operation unit has failed or not can be determined by detecting when at least one of the intake and exhaust valves is opened/closed. A variable valve timing apparatus capable of detecting failure can thus be provided.

Preferably the first operation unit is smaller in strength than the second operation unit.

In accordance with the present invention the first operation unit is provided to be smaller in strength than the second operation unit. This allows a failure to be caused earlier in the first operation unit capable of detection of failure than the second operation unit. This can prevent the second operation unit from having a failure while the first operation unit normally operates and the failure cannot be detected.

Still preferably the valve is driven by a camshaft. The first and second operation unit are link mechanisms connected to the camshaft to rotate the camshaft and actuated by an actuator. When at least one of the intake and exhaust valves should be opened/closed is changed as the camshaft is rotated by the actuator via the link mechanism.

In accordance with the present invention a failure can be detected which arises in a link mechanism actuated by an actuator to cause a camshaft to rotate to change when at least one of the intake and exhaust valves should be opened/closed.

The present invention in another aspect provides a variable valve timing apparatus changing when at least one of an intake valve and an exhaust valve should be opened/closed. The variable valve timing apparatus includes: a first operation unit provided to change when at least one of the intake and exhaust valves should be opened/closed by an amount of variation depending on an amount of operation thereof; a second operation unit provided to change when a valve identical to at least one of the intake and exhaust valves controlled by the first mechanism should be opened/closed by an amount of variation depending on an amount of operation thereof; and a first limiter unit limiting the first operation unit in operation such that the first operation unit is operable only within a range smaller than the second operation unit is operable for a direction retarding when at least one of the intake and exhaust valves should be opened/closed; a second limiter unit limiting the second operation unit in operation such that the second operation unit is operable only within a range smaller than the first operation unit is operable for a direction advancing when at least one of the intake and exhaust valves should be opened/closed.

In accordance with the present invention when at least one of intake and exhaust valves should be opened/closed is changed by an amount of variation depending on an amount of operation of a first operation unit (e.g., a first link mechanism) and a second operation unit (e.g., a second link mechanism). If one of the operation units is damaged and cannot operate normally, the other operation unit can change when at least one of the intake and exhaust valves should be opened/closed. The first operation unit can operate within a range limited by a first limiter unit to be smaller than the second operation unit can for a direction retarding when at least one of the intake and exhaust valves should be opened/closed. The second operation unit can operate within a range limited by a second limiter unit to be smaller than the first operation unit can for a direction advancing when at least one of the intake and exhaust valves should be opened/closed. If the first operation unit is not damaged or the like and normally operates, when at least one of the intake and exhaust valves should be opened/closed can be retarded until the first operation unit is limited in operation by the first limiter unit. In contrast, if the first operation unit is damaged and cannot operate normally, the first operation unit is not limited in operation by the limiter unit and when at least one of the intake and exhaust valves should be opened/closed can further be retarded beyond the first operation unit's operable range. Similarly, if the second operation unit is not damaged or the like and normally operates, when at least one of the intake and exhaust valves should be opened/closed can be advanced until the second operation unit is limited in operation by the second limiter unit. In contrast, if the second operation unit is damaged and cannot operate normally, the second operation unit is not limited in operation by the second limiter unit and when at least one of the intake and exhaust valves should be opened/closed can further be advanced beyond the second operation unit's operable range. As such, whether the first or second operation unit has failed or not can be determined by detecting when at least one of the intake and exhaust valves is opened/closed. A variable valve timing apparatus capable of detecting failure can thus be provided.

Preferably the valve is driven by a camshaft. The first and second operation unit are link mechanisms connected to the camshaft to rotate the camshaft and actuated by an actuator. When at least one of the intake and exhaust valves should be opened/closed is changed as the camshaft is rotated by the actuator via the link mechanism.

In accordance with the present invention a failure can be detected which arises in a link mechanism actuated by an actuator to cause a camshaft to rotate to change when at least one of the intake and exhaust valves should be opened/closed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematically shows a configuration of an engine of a vehicle on which the present variable valve timing apparatus in a first embodiment is mounted.

FIG. 2 shows a map defining the phase of an intake camshaft.

FIG. 3 is a cross section showing an intake WT mechanism.

FIG. 4 is a cross section along A-A in FIG. 3.

FIG. 5 is a (first) cross section along B-B in FIG. 3.

FIG. 6 is a (second) cross section along B-B in FIG. 3.

FIG. 7 is a cross section along C-C in FIG. 3.

FIG. 8 is a cross section along D-D in FIG. 3.

FIG. 9 is a flowchart representing a structure of a program for control executed by an ECU controlling an intake VVT mechanism of the present variable valve timing apparatus in the first embodiment.

FIG. 10 is a (second) cross section along C-C in FIG. 3.

FIG. 11 is a (third) cross section along C-C in FIG. 3.

FIG. 12 is a (first) cross section of a link mechanism of the present variable valve timing apparatus in a second embodiment.

FIG. 13 is a (second) cross section of the link mechanism of the present variable valve timing apparatus in the second embodiment.

FIG. 14 is a (first) cross section of a guide plate of the present variable valve timing apparatus in a third embodiment.

FIG. 15 is a flowchart representing a structure of a program for control executed by the ECU controlling the intake VVT mechanism of the present variable valve timing apparatus in the third embodiment.

FIG. 16 is a (second) cross section of a guide plate of the present variable valve timing apparatus in the third embodiment.

FIG. 17 is a (third) cross section of the guide plate of the present variable valve timing apparatus in the third embodiment.

FIG. 18 is a cross section of a limiter pin limiting a range within which a link mechanism is operable in the present variable valve timing apparatus in another embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

With reference to the drawings, embodiments of the present invention are hereinafter described. In the following description, like components are denoted by like reference characters. They are also named identically and function identically. Therefore, a detailed description thereof is not repeated.

First Embodiment

Referring to FIG. 1, a description is given of an engine of a vehicle on which a variable valve timing apparatus is mounted, according to a first embodiment of the present invention.

An engine 1000 is a V-type 8-cylinder engine having an “A” bank 1010 and a “B” bank 1012 each including a group of four cylinders. Here, any engine other than the V8 engine may be used.

Into engine 1000, air is sucked from an air cleaner 1020. The quantity of sucked air is adjusted by a throttle valve 1030. Throttle valve 1030 is an electronic throttle valve driven by a motor.

The air is supplied through an intake manifold 1032 into a cylinder 1040. The air is mixed with fuel in cylinder 1040 (combustion chamber). Into cylinder 1040, the fuel is directly injected from an injector 1050. In other words, injection holes of injector 1050 are provided within cylinder 1040.

The fuel is injected in the intake stroke. When the fuel is injected is not limited to the intake stroke. Further, in the present embodiment, engine 1000 is described as a direct-injection engine having injection holes of injector 1050 that are disposed within cylinder 1040. However, in addition to direct-injection (in-cylinder) injector 1050, a port injector may be provided. Moreover, only the port injector may be provided.

The air-fuel mixture in cylinder 1040 is ignited by a spark plug 1060 and accordingly burned. The air-fuel mixture after burned, namely exhaust gas, is cleaned by a three-way catalyst 1070 and thereafter discharged to the outside of the vehicle. The air-fuel mixture is burned to press down a piston 1080 and thereby rotate a crankshaft 1090.

At the top of cylinder 1040, an intake valve 1100 and an exhaust valve 1110 are provided. Intake valve 1100 is driven by an intake camshaft 1120. Exhaust valve 1110 is driven by an exhaust camshaft 1130. Intake camshaft 1120 and exhaust camshaft 1130 are coupled by such parts as a chain and gears to be rotated at the same rotational speed.

Intake valve 1100 has its phase (or when it should be opened/closed) controlled by an intake VVT mechanism 2000 provided to intake camshaft 1120. Exhaust valve 1110 has its phase (or when it should be opened/closed) controlled by an exhaust VVT mechanism 3000 provided to exhaust camshaft 1130.

In the present embodiment, intake camshaft 1120 and exhaust camshaft 1130 are rotated by the VVT mechanisms to control respective phases of intake valve 1100 and exhaust valve 1110. Here, the phase control method is not limited to the aforementioned one.

Intake VVT mechanism 2000 is operated by an electric motor 2060 (not shown in FIG. 1). Electric motor 2060 is controlled by an ECU 4000. The current and voltage of electric motor 2060 are detected by an ammeter (not shown) and a voltmeter (not shown) and the measurements are input to ECU 4000.

Exhaust VVT mechanism 3000 is hydraulically operated. Here, intake VVT mechanism 2000 may be hydraulically operated while exhaust VVT mechanism 3000 may be operated by an electric motor.

To ECU 4000, signals indicating the rotational speed and the crank angle of crankshaft 1090 are input from a crank angle sensor 5000. Further, to ECU 4000, signals indicating respective phases of intake camshaft 1120 and exhaust camshaft 1130 (phase: the camshaft position in the rotational direction) are input from a cam position sensor 5010.

Furthermore, to ECU 4000, a signal indicating the water temperature (coolant temperature) of engine 1000 from a coolant temperature sensor 5020 as well as a signal indicating the quantity of intake air (quantity of air taken or sucked into engine 1000) of engine 1000 from an airflow meter 5030 are input.

Based on these signals input from the sensors as well as a map and a program stored in a memory (not shown), ECU 4000 controls the throttle angle, the timing of ignition, the timing of injection of fuel, the quantity of fuel injected, the phase of intake valve 1100, and the phase of exhaust valve 1110 for example, so that engine 1000 is operated in a desired operating state.

In the present embodiment, ECU 4000 determines the phase of intake valve 1100 based on the map as shown in FIG. 2 that uses the engine speed NE and the intake air quantity KL as parameters. A plurality of maps for respective coolant temperatures are stored for determining the phase of intake valve 1100.

In the following, a further description is given of intake VVT mechanism 2000. As shown in FIG. 3, intake VVT mechanism 2000 is comprised of a sprocket 2010, a cam plate 2020, a link mechanism (A) 2030, a link mechanism (B) 2130, a guide plate 2040, a cycloid speed reducer 2050, and electric motor 2060.

Sprocket 2010 is coupled via a chain or the like to crankshaft 1090. The rotational speed of sprocket 2010 is half the rotational speed of crankshaft 1090. Intake camshaft 1120 is provided concentrically with the rotational axis of sprocket 2010 and rotatably relative to sprocket 2010.

Cam plate 2020 is coupled to intake camshaft 1120 with a pin (1) 2070. Cam plate 2020 rotates, on the inside of sprocket 2010, together with intake camshaft 1120. Here, cam plate 2020 and intake camshaft 1120 may be integrated into one unit.

Link mechanism (A) 2030 is comprised of an arm (A1) 2031 (not shown in FIG. 3) and an arm (A2) 2032 (not shown in FIG. 3). Link mechanism (B) 2130 is comprised of an arm (B1) 2131 and an arm (B2) 2132.

As shown in FIG. 4 which is a cross section along A-A in FIG. 3, arms (A1) 2031 and (B1) 2131 are provided within sprocket 2010 so that the arms are point symmetric to each other with respect to the rotational axis of intake camshaft 1120. Arms (A1) 2031 and (B1) 2131 are coupled to sprocket 2010 so that the arms can swing about a pin (2) 2072.

As shown in FIG. 5 which is a cross section along B-B in FIG. 3 and as shown in FIG. 6 showing the state where the phase of intake valve 1100 is advanced with respect to the state in FIG. 5, arm (A1) 2031 and cam plate 2020 are coupled by arm (A2) 2032. Arm (B1) 2131 and cam plate 2020 are coupled by arm (B2) 2132.

Arm (A2) 2032 is supported so that the arm can swing about a pin (3) 2074 and with respect to arm (A1) 2031. Similarly, arm (B2) 2132 is supported so that the arm can swing about a pin (3) 2074 and with respect to arm (B1) 2131. Further, arms (A2) 2032 and (B2) 2132 are supported so that the arms can swing about a pin (4) 2076 and with respect to cam plate 2020.

Link mechanisms (A) 2030 and (B) 2130 cause intake camshaft 1120 to rotate relative to sprocket 2010 and thereby changes the phase of intake valve 1100.

In the present embodiment a pair of link mechanisms (A) 2030 and (B) 2130 can be provided. As such, if one of link mechanisms (A) 2030 and (B) 2130 is damaged or the like and thus broken, the other link mechanism can operate to change the phase of intake valve 1100.

Referring back to FIG. 3, at a surface of link mechanism (A) 2030 (arm (A2) 2032) that is a surface thereof facing guide plate 2040, a control pin (A) 2034 is provided. Similarly, at a surface of link mechanism (B) 2130 (arm (B2) 2132) that is a surface thereof facing guide plate 2040, a control pin (B) 2134 is provided.

Control pins (A) 2034 and (B) 2134 are provided concentrically with pin (3) 2074. Control pin (A) 2034 slides in a guide groove (A) 2041 provided in guide plate 2040. Control pin (B) 2134 slides in a guide groove (B) 2042 provided in guide plate 2040.

Control pins (A) 2034 and (B) 2134 slide in guide grooves (A) 2041 and (B) 2042 of guide plate 2040 to move in the radial direction. Control pins (A) 2034 and (B) 2134 sliding in the radial direction cause intake camshaft 1120 to rotate relative to sprocket 2010.

As shown in FIG. 7 which is a cross section along C-C in FIG. 3, guide grooves (A) 2041 and (B) 2042 are formed to incline at a predetermined angle to the radial direction so that rotation of guide plate 2040 causes control pins (A) 2034 and (B) 2134 to move in the radial direction. Here, guide grooves (A) 2041 and (B) 2042 may be formed to have a geometry other than described above.

As control pins (A) 2034 and (B) 2134 are moved further in the radial direction from the axial center of guide plate 2040, the phase of intake valve 1100 is retarded to a greater extent. In other words, the amount of variation of the phase has a value corresponding to the amount of operation of link mechanisms (A) 2030 and (B) 2130 generated as control pins (A) 2034 and (B) 2134 positionally, radially move.

Note that the phase of intake valve 1100 may be advanced to a greater extent as control pins (A) 2034 and (B) 2134 are moved further in the radial direction from the axial center of guide plate 2040.

Guide groove (A) 2041 is shorter than guide groove (B) 2042. Guide grooves (A) 2041 and (B) 2042 are different only in length. Other than that, they are provided in point symmetry with respect to the axial center of guide plate 2040.

As shown in FIG. 7, control pin (B) 2134 is detached from an end of guide groove (B) 2042 when control pins (A) 2034 and (B) 2134 are moved in a direction allowing the phase to be retarded until control pin (A) 2034 abuts against an end of guide groove (A) 2041.

Note that control pin (B) 2134 may be detached from the end of guide groove (B) 2042 when control pins (A) 2034 and (B) 2134 are moved in a direction allowing the phase to be advanced until control pin (A) 2034 abuts against the end of guide groove (A) 2041.

When control pin (A) 2034 abuts against an end of guide groove (A) 2041, link mechanism (A) 2030 is limited in operation in the direction allowing the phase to be retarded. Therefore, if link mechanism (A) 2030 normally operates, the phase for which control pin (A) 2034 abuts against the end of guide groove (A) 2041 will be the phase of the maximally retarded angle.

Furthermore, when control pins (A) 2034 and (B) 2134 are moved in the direction allowing the phase to be advanced, the phase for which control pin (A) 2034 abuts against the end of guide groove (A) 2041 and control pin (B) 2134 abuts against the end of guide groove (B) 2042 will be the phase of the maximally advanced angle.

Referring back to FIG. 3, in guide plate 2040, a plurality of depressed portions 2044 are provided in its surface facing cycloid speed reducer 2050, for coupling guide plate 2040 and cycloid speed reducer 2050 to each other.

Cycloid speed reducer 2050 is comprised of a ring gear 2052 and a planetary gear 2054. Ring gear 2052 is fixed with respect to sprocket 2010 so that the gear rotates together with sprocket 2010.

Planetary gear 2054 has a plurality of protruded portions 2056 thereon that are received in depressed portions 2044 of guide plate 2040. Planetary gear 2054 is supported rotatably about an eccentric axis 2066 of a coupling 2062 formed eccentrically with respect to an axial center 2064 of an output shaft of electric motor 2060.

FIG. 8 shows a cross section along D-D in FIG. 3. Planetary gear 2054 has teeth smaller in number than ring gear 2052 by one. Planetary gear 2054 is provided so that a part of the teeth thereof meshes with ring gear 2052.

When electric motor 2060 causes coupling 2062 to rotate about axial center 2064 and relative to ring gear 2052, accordingly planetary gear 2054 as a whole rotates about axial center 2064 while planetary gear 2054 rotates about eccentric axis 2066. The rotational motion of planetary gear 2054 causes guide plate 2040 to rotate relative to sprocket 2010 and thus the phase of intake valve 1100 is changed.

If the rotational speed of the output shaft of electric motor 2060 is identical to the rotational speed of sprocket 2010, coupling 2062 and planetary gear 2054 rotate at the same rotational speed as that of ring gear 2052 (sprocket 2010). In this case, guide plate 2040 rotates at the same rotational speed as that of sprocket 2010 and accordingly the phase of intake valve 1100 is maintained.

Reference will now be made to FIG. 9 to describe a structure of a program for control that ECU 4000 controlling intake VVT mechanism 2000 executes to determine whether intake VVT mechanism 2000 has failed. The program described hereinafter is executed at a predetermined time, such as when an ignition switch (not shown) is turned on to start engine 1000, the engine is idle, or the like.

In step (S) 100 ECU 4000 controls intake VVT mechanism 2000 to maximally retard the phase of intake valve 1100 (or when the valve is opened/closed). For example, electric motor 2060 is operated in a direction allowing the phase to be retarded until the drive current of electric motor 2060 rapidly increases (or a lock current is detected).

In S110 ECU 4000 detects the phase of intake valve 1100 (or that of intake camshaft 1120) as based on a signal transmitted from crank angle sensor 5000 and cam position sensor 5010.

In S120 ECU 4000 determines whether a phase more retarded than that for which control pin (A) 2034 abuts against an end of guide groove (A) 2041 is detected. If so (YES in S120) the control proceeds to S130. Otherwise (NO in S120), the control proceeds to S140.

In S130 ECU 4000 determines that intake VVT mechanism 2000 has failed. At the time, a decision is made that link mechanism (A) 2030 has failed. In S140 ECU 4000 determines that intake VVT mechanism 2000 has link mechanism (A) 2030 operating normally.

As based on the structure and flowchart as described above, ECU 4000 operates to control the valuable valve timing apparatus in the present embodiment, as will be described hereinafter.

Intake VVT mechanism 2000 is controlled to maximally retard the phase of intake valve 1100 at a predetermined time (S100) and the current phase is detected (S110).

If intake VVT mechanism 2000 has link mechanism (A) 2030 undamaged and hence in a condition allowing normal operation, then, as shown in FIG. 10, control pin (A) 2034 abuts against an end of guide groove (A) 2041 and control pin (B) 2134 is detached from an end of guide groove (B) 2042.

In this condition, the phase will not further be retarded. As such, the detected phase matches that for which control pin (A) 2034 abuts against the end of guide groove (A) 2041 (NO in S120).

In that case, it can be said that link mechanism (A) 2030 is normally operating. Accordingly a decision is made that intake VVT mechanism 2000 has link mechanism (A) 2030 operating normally (S140).

If intake VVT mechanism 2000 has link mechanism (A) 2030 damaged and thus broken or similarly failed, control pin (A) 2034 abutting against an end of guide groove (A) 2041 does not limit the operation of link mechanism (A) 2030. Accordingly, the rotation of intake camshaft 1120 relative to sprocket 2010 is not limited.

In that case, as shown in FIG. 11, until control pin (B) 2134 abuts against an end of guide groove (B) 2042 link mechanism (B) 2130 operates and intake camshaft 1120 is rotated relative to sprocket 2010.

If in that condition a phase is detected, it will be a phase more retarded than that for which control pin (A) 2034 abuts against the end of guide groove (A) 2041. As such, if a phase more retarded than that for which control pin (A) 2034 abuts against the end of guide groove (A) 2041 is detected (YES in S120) then a decision is made that the VVT mechanism 2000 has failed at link mechanism (A) 2030 (S130). A failure arising in intake VVT mechanism 2000 at link mechanism (A) 2030 can thus be detected.

Thus the present embodiment provides a variable valve timing apparatus implemented by an intake VVT mechanism in which a guide groove (A) along which a control pin (A) of a link mechanism (A) slides is shorter, for a direction allowing the intake valve's phase to be retarded, than a guide groove (B) along which a control pin (B) of a link mechanism (B) slides. If link mechanism (A) is not damaged or the like and normally operates, the phase can be retarded until control pin (A) of link mechanism (A) abuts against an end of guide groove (A). If link mechanism (A) is damaged and broken, then the phase can further be retarded until control pin (B) of link mechanism (B) abuts against an end of guide groove (B). Thus whether link mechanism (A) has failed or not can be determined from a phase detected when the intake VVT mechanism is controlled to allow the phase to be maximally retarded. As a result a failure arising in the intake VVT mechanism can be detected.

Second Embodiment

A second embodiment of the present invention will be described hereinafter. The present embodiment differs from the first embodiment in that link mechanism (A) is formed to be smaller in strength than link mechanism (B).

The remaining hardware and control structures are identical to those described in the first embodiment. They are also identical in function. Accordingly they will not be described repeatedly in detail.

As shown in FIG. 12, link mechanism (A) 2030 has arm (A2) 2032 provided with a hole 2036 to be smaller in strength than arm (B2) 2132 of link mechanism (B) 2130.

Note that in place of or in addition to hole 2036, link mechanism (A) 2030 may have arm (A2) 2032 having a side surface notched 2038, as shown in FIG. 13, to reduce arm (A2) 2032 in strength.

Furthermore, in place of or in addition to arm (A2) 2032, arm (A1) 2031 may be provided with a hole or notched to be smaller in strength than arm (B1) 2131.

Furthermore, link mechanism (A) 2030 may have pins (2) 2072, (3) 2074 and (4) 2076 smaller in strength than pins (2) 2072, (3) 2074 and (4) 2076 of link mechanism (B) 2130.

This allows a damage or a similar failure to be caused earlier in link mechanism (A) 2030 capable of detecting that failure has arisen than in link mechanism (B) 2130. This can prevent link mechanism (B) 2130 having a failure while link mechanism (A) 2030 normally operates and the failure cannot be detected.

Third Embodiment

A third embodiment of the present invention will be described hereinafter. The present embodiment differs from the first embodiment in that control pin (A) is detached from an end of guide groove (A) when control pins (A) and (B) are moved in a direction allowing the phase to be advanced until control pin (B) abuts against an end of guide groove (B).

The remaining hardware and control structures are identical to those described in the first or second embodiment. They are also identical in function. Accordingly they will not be described repeatedly in detail.

As shown in FIG. 14, in the present embodiment, as well as the first embodiment, control pin (B) 2134 is detached from an end of guide groove (B) 2142 when control pins (A) 2034 and (B) 2134 are moved in a direction allowing the phase to be retarded until control pin (A) 2034 abuts against an end of guide groove (A) 2141.

In the present embodiment, in contrast to the first embodiment, guide groove (B) 2142 along which control pin (B) 2134 of link mechanism (B) 2130 slides is shorter, for a direction allowing the phase of intake valve 1100 to be advanced, than guide groove (A) 2141 along which control pin (A) 2034 of link mechanism (A) 2030 slides.

As such, control pin (A) 2034 is detached from an end of guide groove (A) 2141 when control pins (A) 2034 and (B) 2134 are moved in a direction allowing the phase to be advanced until control pin (B) 2134 abuts against an end of guide groove (B) 2142.

When control pin (B) 2134 abuts against the end of guide groove (B) 2142, link mechanism (B) 2130 is limited in operation in the direction allowing the phase to be advanced. Therefore, if link mechanism (B) 2130 normally operates, the phase for which control pin (B) 2134 abuts against the end of guide groove (B) 2142 will be the phase of the maximally advanced angle.

Reference will now be made to FIG. 15 to describe a structure of a program for control that ECU 4000 controlling intake VVT mechanism 2000 executes to determine whether intake VVT mechanism 2000 has failed. Note that the program described hereinafter is executed before or after that in the first embodiment is executed.

In S200 ECU 4000 controls intake VVT mechanism 2000 to maximally advance the phase of intake valve 1100 (or when the valve is opened/closed). For example, electric motor 2060 is operated in a direction allowing the phase to be advanced until the drive current of electric motor 2060 rapidly increases (or a lock current is detected).

In S210 ECU 4000 detects the phase of intake valve 1100 (or that of intake camshaft 1120) as based on a signal transmitted from crank angle sensor 5000 and cam position sensor 5010.

In S220 ECU 4000 determines whether a phase more advanced than that for which control pin (B) 2134 abuts against an end of guide groove (B) 2142 is detected. If so (YES in S220) the control proceeds to S230. Otherwise (NO in S220), the control proceeds to S240.

In S230 ECU 4000 determines that intake VVT mechanism 2000 has failed. At the time, a decision is made that link mechanism (B) 2130 has failed. In S240 ECU 4000 determines that intake VVT mechanism 2000 has link mechanism (B) 2130 operating normally.

As based on the structure and flowchart as described above, ECU 4000 operates to control the valuable valve timing apparatus in the present embodiment, as will be described hereinafter.

Intake VVT mechanism 2000 is controlled to maximally advance the phase of intake valve 1100 (S200) and the current phase is detected (S210).

If intake VVT mechanism 2000 has link mechanism (B) 2130 undamaged and hence in a condition allowing normal operation, then, as shown in FIG. 16, control pin (B) 2134 abuts against an end of guide groove (B) 2142 and control pin (A) 2034 is detached from an end of guide groove (A) 2141.

In this condition, the phase will not further be advanced. As such, the detected phase matches that for which control pin (B) 2134 abuts against the end of guide groove (B) 2142 (NO in S220).

In that case, it can be said that link mechanism (B) 2130 is normally operating. Accordingly a decision is made that intake VVT mechanism 2000 has link mechanism (B) 2130 operating normally (S240).

If intake VVT mechanism 2000 has link mechanism (B) 2130 damaged and thus broken or similarly failed, control pin (B) 2134 abutting against an end of guide groove (B) 2142 does not limit the operation of link mechanism (B) 2130. Accordingly, the rotation of intake camshaft 1120 relative to, sprocket 2010 is not limited.

In that case, as shown in FIG. 17, until control pin (A) 2034 abuts against an end of guide groove (A) 2141 link mechanism (A) 2030 operates and intake camshaft 1120 is rotated relative to sprocket 2010.

If in that condition a phase is detected, it will be a phase more advanced than that for which control pin (B) 2134 abuts against the end of guide groove (B) 2142. As such, if a phase more retarded than that for which control pin (B) 2134 abuts against the end of guide groove (B) 2142 is detected (YES in S220) then a decision is made that the VVT mechanism 2000 has failed at link mechanism (B) 2130 (S230).

Thus, similarly as has been described in the first embodiment, a failure arising in intake VVT mechanism 2000 at link mechanism (A) 2030 can be detected, and so can that arising at link mechanism (B) 2130.

Thus the present embodiment provides a variable valve timing apparatus implemented by an intake VVT mechanism in which a guide groove (A) along which a control pin (A) of a link mechanism (A) slides is shorter, for a direction allowing the intake valve's phase to be retarded, than a guide groove (B) along which a control pin (B) of a link mechanism (B) slides and guide groove (B) along which control pin (B) of link mechanism (B) slides is shorter, for a direction allowing the intake valve's phase to be advanced, than guide groove (A) along which control pin (A) of link mechanism (A) slides. If link mechanism (A) is not damaged or the like and normally operates, the phase can be retarded until control pin (A) of link mechanism (A) abuts against an end of guide groove (A). If link mechanism (A) is damaged and broken, then the phase can further be retarded until control pin (B) of link mechanism (B) abuts against an end of guide groove (B). Similarly, if link mechanism (B) is not damaged or the like and normally operates, the phase can be advanced until control pin (B) of link mechanism (B) abuts against an end, of guide groove (B). If link mechanism (B) is damaged and broken, then the phase can further be advanced until control pin (A) of link mechanism (A) abuts against an end of guide groove (A). Thus whether link mechanism (A) or link mechanism (B) has failed or not can be determined from a phase detected when the intake VVT mechanism is controlled to allow the phase to be maximally retarded or advanced. As a result a failure arising in the intake VVT mechanism can be detected.

Note that while in the first to third embodiments intake VVT mechanism 2000 has two link mechanisms, it may have three or more link mechanisms.

Furthermore in exhaust VVT mechanism 3000 two or more link mechanisms may be employed to change the phase of exhaust valve 1110 and detect a failure of a link mechanism in exhaust VVT mechanism 3000.

Furthermore, in place of or in addition to a link mechanism, a mechanism other than the link mechanism may be employed to change a phase of intake valve 1100, exhaust valve 1100 or the like and detect a failure arising in that mechanism.

Other Embodiment

In addition to guide grooves (A) 2041 and 2141 and (B) 2042 and 2142 provided in guide plate 2040, limiter pins (1) 2200, (2) 2202 and the like may be employed to limit the range within which link mechanisms (A) 2030, (B) 2130 and the like are operable, as shown in FIG. 18.

In FIG. 18 limiter pin (1) 2200 limits link mechanism (A) 2030 in operation so that, for a direction for retard, link mechanism (A) 2030 is operable within a range smaller than link mechanism (B) 2130 is.

Limiter pin (2) 2202 limits link mechanism (B) 2130 in operation so that, for a direction for advance, link mechanism (B) 2130 is operable within a range smaller than link mechanism (A) 2030 is.

Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims. 

1. A variable valve timing apparatus changing when at least one of an intake valve and an exhaust valve should be opened/closed, comprising a first operation unit provided to change when said at least one of said intake and exhaust valves should be opened/closed by an amount of variation depending on an amount of operation thereof; a second operation unit provided to change when a valve identical to said at least one of said intake and exhaust valves controlled by said first operation unit should be opened/closed by an amount of variation depending on an amount of operation thereof; and a limiter unit limiting said first operation unit in operation such that said first operation unit is operable only within a range smaller than said second operation unit is operable, wherein said first operation unit is smaller in strength than said second operation unit.
 2. (canceled)
 3. The variable valve timing apparatus according to claim 1, wherein: said valve is driven by a camshaft; said operation unit is a link mechanism connected to said camshaft to rotate said camshaft and actuated by an actuator; and when said at least one of said intake and exhaust valves should be opened/closed is changed as said camshaft is rotated by said actuator via said link mechanism.
 4. A variable valve timing apparatus changing when at least one of an intake valve and an exhaust valve should be opened/closed, comprising a first operation unit provided to change when said at least one of said intake and exhaust valves should be opened/closed by an amount of variation depending on an amount of operation thereof; a second operation unit provided to change when a valve identical to said at least one of said intake and exhaust valves controlled by said first operation unit should be opened/closed by an amount of variation depending on an amount of operation thereof; and a first limiter unit limiting said first operation unit in operation such that said first operation unit is operable only within a range smaller than said second operation unit is operable for a direction retarding when said at least one of said intake and exhaust valves should be opened/closed; a second limiter unit limiting said second operation unit in operation such that said second operation unit is operable only within a range smaller than said first operation unit is operable for a direction advancing when said at least one of said intake and exhaust valves should be opened/closed.
 5. The variable valve timing apparatus according to claim 4, wherein: said valve is driven by a camshaft; said operation unit is a link mechanism connected to said camshaft to rotate said camshaft and actuated by an actuator; and when said at least one of said intake and exhaust valves should be opened/closed is changed as said camshaft is rotated by said actuator via said link mechanism. 